1. Field of the Invention
This invention relates to an apparatus for forming a wheel rim, and in particular to an apparatus for producing a wheel rim from a cylindrical blank.
2. Description of the Prior Art
Vehicle wheel rims are conventionally manufactured from sheet metal blanks, which may be cold rolled to impart the desired profile to the blanks, cut to the required length, soldered to connect the ends of the blanks and finally placed in a so-called expander to give the rims their final dimensions. Such a method of producing wheel rims is relatively expensive and complicated, requiring two or more large machines for forming and closing the blanks, and for imparting the desired final configuration and dimensions to the rims.
Alternatively, the rims are formed from cylindrical blanks using a machine including an annular die having an internal profile identical to the desired final profile of the rims, and a turntable rotatable in the annular die. Such a machine is disclosed by U.S. Pat. No. 2,933,124 which issued to W. E. Benson and G. E. Benson on Apr. 19, 1960. The turntable includes a pair of profiled primary rollers which are radially displaceable for pressing against a cylindrical blank to deform the latter agaisnt the interior surface of the female die. With the male die rotating, the primary rollers are moved outwardly simultaneously by a spreader roller, which is operated by a hydraulic cylinder or by a rack and pinion arrangement to impart the basic rim configuration to the blank. The rim is completed, i.e. the rim beads are formed by means of eccentric discs, eccentrics or separate flange formation rollers.
When forming conventional wheel rims, a machine of the type disclosed by the above-identified United States patent is preferred. However, it is unlikely that the Benson machine in its simplest form whould be capable of accurately forming wheel rims from thick blanks, e.g. 1/4 inch steel blanks used for truck wheel rims. The forces involved in the formation of such a rim are considerable, and the simultaneous movement of a pair of rollers against the blank to form a rim would be difficult if not impossible. Moreover, most forms of the Benson machine are relatively complicated, and consequently expensive to produce. For example, the Benson patent proposes the use of a multi-part annular female die.
Even more important is the fact that, in all forms of the Benson machine, the blank is suspended in the annular die between a central well formation projection on the die and the top and bottom edges of well formation rollers on the turntable. No provision is made for accurately positioning the blank in the annular die. With the Benson arrangment, it is quite likely that the blank would be drawn into the annular central recesses of the rollers unevenly. Moreover, applicants believe that it is quite likely that the blank is stretched during formation in the Benson machine, resulting in a rim of non-uniform thickness. Finally, with the Benson machine, a blank of intermediate diameter is used, i.e. a blank having a diameter between the maximum and minimum diameters of the rim. Thus, the blank must be deformed along its entire length; inwardly at the centre to form the well and outwardly at the top and bottom ends to form the tire beads. The result is a relatively complicated forming process, with accompanying risk of improper rim formation.
Thus, in its simplest form, the Benson machine is at best difficult to operate and in its more sophisticated forms is complicated and expensive to produce.
The Benson patent strongly suggests (column 2, lines 19 to 41) that the use of a rotatable female die is impractical. Applicants have found that such is not the case, and that a relatively simple and inexpensive apparatus for forming a wheel rim from a cylindrical blank can be produced using a rotatable female die and a stationary male die. The present invention relies on the use of separate profiled rollers for deforming a blank stepwise, the rollers being mounted on eccentric shafts which are rotated one at a time to bring selected rollers to bear against the rim sequentially.